The present invention relates to a positive radiation-sensitive mixture containing a compound which forms an acid under the action of actinic radiation, and an acid-cleavable compound.
Positive radiation-sensitive mixtures in which an acid is formed through the action of actinic radiation on a photoinitiator and the acid then, in a secondary reaction, renders the irradiated regions of an acid-cleavable material soluble in an appropriate developer have been known for some time.
Of the acid-cleavable materials employed hitherto in this area, the following have proven successful:
(a) those containing at least one orthocarboxylic ester and/or carboxamide aceta group, it being possible for the compounds to have a polymeric character and for the groups mentioned to occur as linking elements in the main chain or as lateral substituents, PA1 (b) oligomeric or polymeric compounds containing recurring acetal and/or ketal groups in the main chain, PA1 (c) compounds containing at least one enol ether or N-acyliminocarbonate group, PA1 (d) compounds containing silyl ether groups, PA1 (e) compounds containing siylenol ether groups, and PA1 (f) cyclic acetals or ketals of .beta.-keto esters or amides. PA1 R denotes carboxyl, OR' or SR', PA1 R.sub.1 and R.sub.2 are identical or different and denote hydrogen, chorine, bromine, alkyl, which is optionally substituted by aryl, alkoxy, aryloxy, hydroxyl groups or by fluorine atoms; or alkyl, which is optionally substituted by alkoxy, aryloxy, hydroxyl groups or by halogen atoms, PA1 R' denotes hydrogen, alkyl which is optionally substituted by aryl, alkoxy, aryloxy or hydroxyl groups or by fluorine atoms; aryl which is optionally substituted by alkoxy, aryloxy or hydroxyl groups or by halogen atoms; acyl, alkylsulfonyl, arylsulfonyl, alkoxycarbcnyl, triorganosilyl, triorganostannyl or denotes an alkylene, arylene, bisacyl, sulfonyl, alkylenedlsulfonyl, arylene disulfonyl, diorganosilyl or diorganostannyl group whose second valency is bonded to the 0 atom of a further unit of the formula I, it being possible for the alkylene and arylene groups to be substituted in corresponding manner to the alkyl and aryl radicals, and PA1 n denotes 0 to 3, PA1 where PA1 R.sub.3 denotes alkyl, in particular, (C.sub.1 -C.sub.3) alkyl, or aryl, in particular, phenyl
As components of radiation-sensitive mixtures, acid-cleavable compounds of type (a) are described in detail in EP-A-0,022,571 and DE-A-2,610,842; mixtures which contain compounds of type (b) are described in DE-C-2,306,248 and DE-C-2,718,254; compounds of type (c) are mentioned in EP-A-0,006,626 and 0,006,627; compounds belonging to type d) are presented in DE-A-3,544,165 and DE-A-3,601,264; compounds of type (e) can be found in U.S. application Ser. No. 07/243,819 Now U.S. Pat. No. 4,916,046 (corresponding to German Patent Application P 3,730,783.5), filed simultaneously, now U.S. Pat. No. 4,916,046, issued Apr. 10, 1990: compounds of type (f) are mentioned in EP-A-0,202,196.
In DE-A-2,610,842, compounds containing ortho -ester or -amide acetal groups in a radiation-sensitive copying material are described which are used in the production both of printing plates and microelectronic circuits. Investigations have shown that the resolution which is necessary in the submicron region can only be achieved to a limited extent or not at all, using the acid-cleavable compounds outlined therein, which liberate formates of low water solubility on exposure.
The radiation-sensitive copying materials described in DE-A-2,718,254 are also used for lithographic printing plates and for positive resists. They contain, as the acid-cleavable component, an oligomeric compound containing recurring acetal or ketal units, whose alcohol component must be at least dihydric. In addition to the large range, due to the production process, within which the molecular weight or degrees of polymerization of such polyacetals vary, the danger of introduction of contaminants into the radiation-sensitive mixture is particularly critical in the case of these acid-cleavable compounds since distillative purification is no longer possible. Due to the choice of the aldehyde or ketone components, some of the acetals and ketals described result in mixtures which are difficult to develop or allow only a small process window between irradiation and development, generally between 0.1 and 5 hours. Depending on this "holding time", considerable development rate differences occur in some cases and can extend so far that development is no longer possible at all.
Use of a recording material containing an acid-cleavable material of this type results in an unacceptable variation of the process parameters. In addition, the structural resolution is in most cases in need of improvement; this applies in particular when the acetal is too soluble in the developer, for example, in the case of acetals containing 4-hydroxybenzaldehyde as the aldehyde component.
In addition, it has recently been proposed, in contrast to the prior art, to employ cyclic acetals or ketals of .beta.-keto esters or amides as an acid-cleavable material which is stated to be also suitable for use in photoresists (EP-A-0,202,196). A disadvantage of these photoresists is their low radiation sensitivity.